Multifunctional RF systems heighten the spectrum-allocation challenge
Communications systems are rapidly evolving to the point that they are fast becoming multifunction radio-frequency (RF) systems. Engineers are working to leverage commercial off-the-shelf (COTS) technology as well as newly promulgated standards to facilitate the design process for the system that will ultimately have to deal with the shared-spectrum environment.
The shared-spectrum environment is a common challenge that designers face when building communications systems. “It is harsher than ever before, as the radio-frequency (RF) spectrum is becoming more and more crowded,” says Rick Gentile, product manager for phased-array system toolbox and signal processing toolbox for The MathWorks (Natick, Massachusetts).
Yet communications systems are rapidly evolving to the point that “The other trend we’ve seen is that a lot of the communication systems aren’t just communication systems anymore, they’re really multifunctional RF systems that also include radar and electronic warfare capabilities using the same hardware,” Gentile adds.
Ken Karnofsky, senior strategist for signal-processing applications at MathWorks, gives an example: “One scenario that’s happening now is that the U.S. government has auctioned off part of the spectrum for LTE. But if that’s being done in a coastal area that happens to be near a Navy port where the ships are using radars that happen to be operating on the same frequency band, then they have to be able to cope with that interference,” Karnofsky says.
The issue comes down to spectrum allocation, which these days means using cutting-edge technology to take communications systems from their former linear perspective to enabling these systems to cognitively be aware of the spectrum and switching at a moment’s notice to a more secure line.
Currently used signal-processing techniques need to evolve as users inundate the spectrum and commercial standards such as LTE show promise for military users.
“For somebody who’s designing and working on radar systems to suddenly learn the LTE standard well enough to be able to deal with that interference is a massive task. It’s thousands of pages,” Karnofsky asserts. “Teams are looking to software and tools to help them come up to speed more quickly and just deal with the aspects of the standard that are relevant to their problem rather than having to master the entire process.”
The tools are the key to solving that complexity problem. Current signal-processing techniques to mitigate interference in communications systems include “using antenna arrays and beamforming to try to concentrate the power of a signal that’s directed towards a specific target or receiver and avoids interfering with other devices that may be emitting in that frequency band,” Karnofsky says.
“Part of the beamforming capability is to strengthen the signal that you’re looking for, but also it gives you the ability to eliminate the interference sources themselves by designing the beam pattern appropriately,” Gentile adds.
However, the user still needs to understand the difference between intentional and unintentional interference. Karnofsky explains, “For instance, you might be in an environment where you have to deal with transmissions from other wireless devices in the same spectrum or frequency.”
This scenario often occurs in an urban environment, where military and commercial users are sharing the spectrum.
Communications device designers today are using all of the technology that is available, including consumer or commercial technology. Technology first used in the commercial or consumer space has in the past enabled military technology. “Some of the commercial hardware actually has the attributes that people are looking for in terms of being able to handle frequency agility and other kinds of adaptive techniques that are needed,” Karnofsky adds. “One of the challenges is working with that hardware and being able to build prototypes effectively.”
He goes on to mention that “Another element of COTS technology is leveraging and co-existing with the commercial wireless standards that are out there. I’m thinking particularly of LTE and wireless LAN environments.”
But it’s not just about the standards, it’s also about the tools. During the design and development process, and then when selecting components, “one of the issues is that many of these techniques are using devices that are very highly integrated, where there can be coupling between the antenna elements in large arrays or interacting between the digital and the RF electronics,” Karnofsky says.
Advanced simulation tools can help designers and users get to finished products faster. “With conventional software tools,” Karnofsky says, “there are typically tools designed for specialists [whether digital signal processing specialists, RF, or antenna specialists]. In order to get things done more quickly and take advantage of some of the off-the-shelf hardware that’s available, there’s the need to be able to simulate those different components together to really optimize the overall behavior of the system.
“Today there is a greater reliance on simulation, in particular multidomain simulation, that allows an end-to-end –or sometimes called antennas-to-bits – type of simulation where you’re going from the antenna through the RF and analog part of the system and then into the digital processing system,” Karnofsky says.
The military has the capability to respond to threats at a quicker rate; that’s why it needs to take advantage of the latest, fastest systems and technologies. “They might even be able to design a prototype with the same hardware that they then deploy into the field,” he adds.
|Figure 1: Plots generated using the new MATLAB graphics system, with updated colors, fonts, and styles. Image by MathWorks.|
During both the design and development processes, it is important to find the right tool for the job. At MathWorks, “MATLAB is very broadly used for technical computing, which means developing the algorithms, doing data analysis, and technical programming.” Karnofsky notes.
|Figure 2: MathWorks Introduces Simulink Real-Time, Offering Complete, Integrated Real-Time Simulation and Testing. Image by MathWorks.|
Combining MATLAB with Simulink, which is MathWorks calls a multi-domain simulation environment, Karnofsky states, enables defense and aerospace users “ to generate code, hardware description languages, or C-code for software processors that can be deployed directly into embedded systems on an FPGA or a processor.”
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